Semiconductor devices are electronic circuits fabricated from a semiconductor material, such as silicon. Historically, the density of these circuits has increased at a dramatic pace, doubling every 18-24 months as described by Moore's Law. This ever-increasing density of semiconductor devices is paralleled by an ever-increasing intensity of heat generated by the electronic equipment that utilizes these devices, such as printed circuit boards, servers, routers, and the like. In data centers and other locations that house large quantities of electronic equipment, cooling systems may be utilized to remove this heat. Efficient heat removal may decrease operational costs, increase equipment lifetime, and decrease equipment downtime.
Conventionally, data centers utilize rack-mounted electronic equipment. Each rack may contain forty or more individual pieces of electronic equipment, each of which utilizes electrical power to operate and generates some amount of heat while in operation. For example, each piece of electrical equipment may utilize 250 watts (W) of electrical power to operate, which means that each rack may require 10 kilowatts (KW) or more of electrical power to operate. It is not uncommon for data centers to include dozens or even hundreds of racks and to have power requirements in the megawatt (MW) range. In a conventional data center, the cooling system may comprise direct expansion air conditioning units, which may utilize as much electrical energy as the equipment that it is cooling, i.e. for every 1 KW supplied to the electronic equipment to power the equipment, another 1 KW may be needed to power the cooling system used to cool the equipment. Thus, cooling power requirements may have a significant impact on the overall energy consumption of the facility.
In addition, a direct expansion air conditioning system must be properly sized, or designed, for the heat load that it is designed to receive, such as from the electronic equipment to be cooled. Such a direct expansion air conditioning system only operates at peak efficiency when the actual heat load is at or near the design load. As additional pieces of electronic equipment are installed, such as during the build-out of a data center, the overall heat load may change significantly. In order to maintain effective cooling, the initial installation of cooling equipment may be significantly oversized, requiring it to run at reduced efficiency until the build-out nears completion, which may take months or even years. Alternatively, the cooling equipment may be installed in stages, thereby increasing incremental operating efficiency but requiring frequent and inconvenient construction. Similarly, since the ambient environment in the vicinity of the electronic equipment may fluctuate with periodic, seasonal, and/or daily temperature, pressure, and/or relative humidity fluctuations, the direct expansion air conditioning system may be sized for the maximum expected heat load based on worst-cast ambient environmental conditions, requiring it to run at a reduced efficiency level when the heat load is less than the maximum expected heat load.
With such high power requirements and built-in system inefficiencies, it may be not only costly, but also difficult, to obtain a reliable source of electricity. In addition, municipalities may place overall energy usage budgets on data centers in an effort to curb environmental impacts and ensure that power is available for other uses. Under these circumstances, any decrease in cooling power requirements may translate directly to the potential for the installation of additional electronic equipment, thereby increasing the revenue potential and/or capabilities of the data center while maintaining a substantially constant utility cost. Thus, there exists a need for higher efficiency data center cooling systems and methods that decrease the amount of energy needed for cooling while maintaining reliable operation and high efficiency over a wide cooling capacity range.